1. Field of the Invention
The present invention relates generally to a fluid level verification apparatus which is operable to measure the amount of fluid present in a fluid container, such as a tank, machine, or other article of manufacture, and more specifically, to an apparatus which may be manufactured or otherwise fabricated as a kit for use on particular machines or in manufacturing processes; and which minimizes the number of components required; and further to a fluid level verification apparatus which reduces mechanical, thermal and chemical stresses on the apparatus.
2. Description of the Prior Art
The prior art is sated with examples of fluid level verification apparatuses which provide a means for visually verifying or otherwise discovering the fluid levels in an object of interest, such as manufacturing machinery, fluid holding tanks, or other similar assemblies. For example, in certain industrial processes or in certain machines or other articles of manufacture, it is important that particular fluids, such as lubricants, coolants, hydraulic fluids, or other fluid components, be stored in tanks and periodically dispensed from such tanks. Prior art fluid verification devices have typically included a transparent tube or inspection window, which is connected in particular relation to the holding tank, and which provides a quick and convenient means by which an observer may visually verify the level of the fluid present.
While the prior art devices have operated with success, they have been unsatisfactory in several respects.
Gruett, U.S. Pat. No. 5,323,653, assigned to the same assignee as the present application, provides a detailed background of the prior art and describes a fluid level verification apparatus that can be fabricated as a kit and assembled at a remote location. Gruett contemplates an inspection tube having an interior conduit dimensioned to create an interference fit with an o-ring used to hermetically seal the inspection tube to an end member. The Gruett apparatus requires a separate seal on the outer diameter of its glass inspection tube to complete a hermetic seal.
Jackson, U.S. Pat. No. 4,345,468, describes a double tube liquid sight monitor, which incorporates grooving and o-rings to isolate the inspection tube from the environment. However, the Jackson invention is relatively complex and cumbersome, as it requires numerous parts to protect the inspection tube from the stresses caused by the environment. Moreover, the sealing function of the grooves are limited to the insert ends thus requiring the o-rings to rest against the internal and external surfaces of inspection tubes that have no such grooves and the problem of mechanical stress induced by the assembly of the inspection tubes to mating components is not contemplated.
Evans, U.S. Pat. No. 4,050,305, describes an external shield bracket for a fluid flowmeter. The fluid of interest flows through a precision glass tube. An operator is protected from accidental explosion of the inspection tube due to fluid pressure by a protective transparent cover mounted on a U-shaped channel bracket. The Evans invention uses many parts, but fails to protect the inspection tube from the environment. Furthermore, this transparent cover and mounting bracket do not form a hermetic closure for the inspection tube contained therein.
Gruett, U.S. Pat. No. 3,886,796, also assigned to the same assignee as the present application, describes a liquid level gauge with a rigid transparent plastic inspection tube with o-rings seated in grooves located in the end members. The Gruett invention was designed for assembly without the need of o-ring grooves on the exterior or interior portions of the inspection tube. The ends of the inspection tube are restricted and nested in the end members.
Lyden, U.S. Pat. No. 3,540,276, describes a fluid level gauge. The Lyden invention uses an o-ring seal nested in an end member, communicating with the adjacent end of a sight tube. Fluid leaks are minimized by placing the glass sight tube in compression with the o-ring seal nested in the respective end member. The glass sight tube is required because the Lyden invention requires compressive force on the tube. Thus, the design creates inherent mechanical stress, and without utilizing the glass sight tube, adapts poorly to thermal, environmental and chemical expansion cycles and therefore is susceptible to leakage.
Lukas, U.S. Pat. No. 3,455,163, describes a liquid level gauge where the apparatus is backwardly attached to the liquid tank. The Lukas invention allows for the inspection sight member to be fittingly secured within the support body by means of plugs placed at the ends of the inspection sight member. However, the use of plugs to secure the inspection sight member within the apparatus causes compressive stress on the inspection sight member. Furthermore, the Lukas invention is not easily attached or removed from a liquid tank.
One advantage of most prior art fluid level detection apparatuses is the ease of replacing the inspection sight member without having to replace the rest of the apparatus. However, the trend in recent years is that users of the apparatus are replacing the entire apparatus, even if only the inspection sight member needs to be replaced. Many of the prior art devices are cumbersome and otherwise complex in their overall design, thereby increasing the cost to manufacture, decreasing the reliability and making them difficult to maintain. Further, the prior art is replete with designs that inadequately address the often conflicting requirements of resisting fluid leaks and protecting the inspection tube from mechanical, environmental, thermal and chemical stresses. Therefore, a need exits for a fluid level verification apparatus that is simple to manufacture yet durable and reliable in use.